Campaigners calls for ban on acid stimulation of onshore oil and gas wells


Markwells Wood oil site in the South Downs National Park where the use of acid was proposed. Photo: DrillOrDrop

Friends of the Earth has called for a ban on the use of acid to stimulate the flow of oil and gas in onshore wells.

In a report called The Acid Test, published this week, it said many of the risks linked to acid stimulation were similar to those for fracking, including contamination of groundwater, soil and air, industrialisation of rural areas, noise, increased traffic and earth tremors.

It said current regulations were not strong enough to deal with these risks and there were gaps in knowledge about the chemicals used. Acid stimulation would also contribute to climate change, it said.

As well as ban, Friends of the Earth called for:

  • An assessment of the health and environmental impacts of acid well stimulations in England
  • Identification of chemicals of concern used in all onshore well stimulation operations
  • Government publication of data on the number and type of acid stimulations in England
  • A requirement for exploration companies to state explicitly in planning applications whether they want to use acid and for what purpose.

Oil and gas companies say they have routinely used acid for decades. But it is not always clear whether this was to clean scale or other deposits from the well, known as acid wash, or to stimulate the flow of hydrocarbons in rock formations.

Acid stimulation is likely at several new oil exploration sites in the Weald basin in southern England, some in protected areas.

Brenda Pollack, south east campaigner for Friends of the Earth, said:

“Residents are right to be worried about the increasing use of acid well stimulation to produce oil and gas in this area. There are a lot of unknowns about the quantities and type of chemicals being used and where they end up.

“It’s clear that we should be reducing fossil fuel use, yet the government is encouraging the industry. Plans to fast track shale gas operations could have implications in the Weald basin which is a known shale oil area.”

What is acid stimulation?

In acid stimulation, companies inject a fluid containing acid and other chemicals into the rock formation. The chemical concentrations are usually 6-18%, higher than the 0.5% concentration used in hydraulic fracturing.

In acid fracturing, one form of acid stimulation, the fluid is injected at pressures high enough to fracture the rocks, as with hydraulic fracturing.

Hydrochloric acid is usually used where the rocks are limestone and hydrofluoric acid in sandstone formations. But sometimes combinations of acids are used.

Key issues

Climate change

Friends of the Earth said:

“[Acid stimulation] is being proposed and is potentially already being used in England to increase fossil fuel production. But, to avoid the worst impacts of climate change, we need to reduce fossil fuel use fast. Increasing fossil fuel production is not compatible with the climate change goals the UK has signed-up to.”


The regulations covering fracking are unlikely to deal with acid stimulation, Friends of the Earth said.

Legislation on hydraulic fracturing applies only where individual fracture treatments use 1,000m3 of water or 10,000m3 in total.

Acid fracking tends to use smaller volumes of fluid, though at higher chemical concentrations. This means there is no automatic requirement to carry out baseline monitoring of methane in groundwater nor monitor methane levels in the air, Friends of the Earth said. There is also no legislation banning surface development of sites using acid stimulation in protected areas like National Parks.

Friends of the Earth said:

“Regulations are not strong enough to cover the risks associated with acid stimulation. No proper environmental risk assessment study appears to have been performed.”

Gaps in knowledge

Friends of the Earth said:

“There are a lot of unknowns about acid stimulation. Whilst we know that many of the chemicals used in the processes can be hazardous, there have been very few studies on the risks and impacts.

“There are significant gaps in knowledge about the chemicals used in the treatments, including overall volumes used, and their toxicity and persistence in the environment, meaning that there are clear risks that residents are right to be concerned about.”

The first toxicological study purely dedicated to acidising was published in the U.S. in 2017. But Friends of the Earth said in England the Environment Agency had not carried out any studies of its own.

“It appears that the Environment Agency has not historically given permits for acid well stimulation operations and is unable to provide data on where acidising has taken place.”

Friends of the Earth added:

“As far as we are aware, there have been no studies to look at the quantities and profiles of chemicals used in acidising operations in England. This means there is a lack of analysis of how much has been used in the past to determine levels of current and future risk.

“Given the number of applications coming forward this must be addressed. The government needs to ensure that adequate reporting is carried out by the industry and that relevant cumulative data on chemical use is publicly available.”

Environmental impacts

Friends of the Earth said:

“acid stimulation could involve hundreds of new oil wells, some in our most precious areas of countryside.

“It is important that there is more clarity when [planning] applications are made so that the public and local decision makers know exactly what type of treatment a developer wants to carry out.”

Industry reaction

Ken Cronin, chief executive of the industry organisation, UK Onshore Oil and Gas, said in response to the Friends of the Earth report:

“The use of acid is a standard water services and oilfield practice for many developments and is clearly outlined in the Environment Agency’s Q&A documentation. Indeed, as Friends of the Earth themselves note, this is a technique that has been widely used since the 1950s.

“Acidisation, both in the water industry and our own, is a regulated practice that allows us to effectively ‘clean’ or improve recovery from a well. It dissolves fine particles and scale, allowing a better flow of what we’re trying to extract. As with household kettles, which need to be treated for limescale build-up, the use of this process merely increases the efficiency of our practices.

“An environmental permit is only issued for this technique if the Environment Agency are satisfied that the proposed activities meet the requirements of all the relevant legislation. Friends of Earth would have you believe that ‘acid’ automatically means a hazard to human health, but according to this report, they would ban us from using formic acid – something commonly found in both bees and nettles.

“According to the OGA, the UK’s oil import dependency is forecast to increase from 30% today to almost 70% by 2035, and the prediction for gas is equally bleak. Under the Committee on Climate Change limits on oil consumption, the use of 46 million tonnes equivalent in 2040 satisfies the Climate Change Act. With oil the biggest sole source of UK energy, instead of proposing ill-informed bans Friends of the Earth should ask themselves why they want us to become a country beholden on others for our basic needs.”

Friends of the Earth summary briefing

Friends of the Earth full briefing

52 replies »

  1. FoE and Nimby activists are now like dictator. If they dont like something or dont fit in their ideology they want to ban it without considering the rights of other or the science.

  2. Well done Friends of the Earth for highlighting the dangers of acid stimulation. And as for acting like dictators, it’s the government that are doing so by forcing these unwanted and dangerous technologies, which are banned in many places, on an increasingly unwilling public. The government are currently planning to allow test wells for future fracking to be built without even applying for planning permission, and then controlling fracking through NSIP. Dictatorship is already here, TW, and it’s the government that is doing it.

  3. Water drilling companies use acid stimulation in the aquifer!!!! And then people drink the water!!!!!! Are they mad? Or dead??

  4. It seems Paul that many of these “charities” don’t need to know what they are talking about anymore. They just assume they are talking to others who will not notice. I am sure it works with some, but I have given up with donating to “charities” that are campaigning organisations, and get controlled by some who have their own agendas. The RSPCA are no better.

    Some well intentioned individuals work diligently in such organisations and do some good work but are undermined.

    Ellie-the last survey showed a decreasingly “unwilling” public (10% I believe). Perhaps that is why the Government decided to speed up the process, or maybe it was the local Councils being unable/unwilling to meet the designated timescales?

    • Martin. These organizations like FoE are no longer function as a charity but more like a political party or lobbyist at best or at worst Russia useful idiot agent.

      • FoE are not a political party and maybe there is a need for organisations like FoE to act like lobbyists to represent their supporters and those opposed to this increasingly undemocratic government. The oil and gas industry, with vast wealth at their disposal, have certainly been working overtime for years, lobbying governments.

        • They have been at it for long enough. I recall FOE objecting to Amoco drilling onshore UK in the 1980s – Hampshire, West Sussex, N Yorks and Lancashire. We drilled a huge section of shale in the Lancs well which no doubt will be of interest to companies now. Our target in those days was a conventional reservoir. We got all our planning permissions and drilled all the wells we applied for. FOE were pretty ineffective then and appear to be the same now. Now they seem happy to throw their members money away fighting appeals and on Judicial Reviews – which they generally lose because they do not have valid objections / evidence. If I was a member of FOE I would be complaining. Perhaps the money does not just come from membership??

  5. The only ‘gaps in knowledge’ is by FOE, leave it to the professionals.

    This really is an embarrassing moment for friends of the earth haha!

  6. And explosives are used in fireworks as well as cluster bombs!!!!! Are they mad? Or dead??
    Or does this comparison also contribute nothing to the dicussion?

    • You do understand that water wells are regularly stimulated with acid? I’ve never heard of anyone dying from drinking water from a UK acidised well, but there are plenty of firework deaths.

      • Al I do indeed understand.

        They briefly use the highest concentrations of HCl (c28%-30% from memory) in a water well then flush the resulting salinated water thoroughly. Of course, as it’s a water well, not so hard to do. Once the water has passed tests it is perfectly safe to drink.

        Acid stimulation in an unconventional oil target like the Kimmeridge in the Weald uses a necklace of shaped explosive charges to perforate the well bore, followed by prolonged, very high pressure (3000-5000psi) acid injection (which is up to the fracture pressure of the rock for what is usually known as matrix acidisation, it would be acid fracking above that pressure).

        Typically 15% HCl is used. Incidentally I’ve seen this has been said to be the same strength as vinigar or coca cola, somtimes stomach acid.
        The actual pH figures are :
        15% HCl pH -0.7
        Coke pH 2.5
        Difference = 3.2 (therefore 1500x stronger).
        So this of course is a very strong acid, Around 200 barrels of it were used to stimulate Horse Hill in the 2016 test, another 300 for the 2018 EWT.
        The intention is to dissolve rock in to achieve the same result as fracking, but at a depth either where fracking isn’t allowed or maybe where it is politically difficult and to be be avoided, certainly at the exploration stage.

        So yes I know acid can be used for various other applications but I prefer to stay focussed on the subject of the article.

        • Dorkonian – when I managed the world’s largest offshore acid fracture stimulations30 years ago (largest at that time) I recall we used 28% HCl and lots of it. Very successful and apparently the wells are still producing now and did not require further stimulation. 10,000 psi and limestone. 1.5% H2S. No problems with the jobs.

          For additional info on HCl the Oxy book is useful:

          Click to access Hydrochloric_Acid_Handbook.pdf

          26% of usage is in the food business; 18% in the oil business.

          • Very interesting Paul, and North Sea oil and gas were of course hugely successful and made a massive contribution to our GDP for decades.

            Can I draw your attention to some differences with the proposed Weald exploration? In no particular order.

            1. We are now committed to restricting man made warming to as near as 1.5 degrees C as possible with a maximum of 2 degrees, to prevent run away climate change leading to mass extinction events.

            2. The target isn’t the limestone you worked with but low permeability shale accessed through the micrite layers running through it. So stimulation will be needed throughout the production and importantly the well density will be similar to the Bakken (according to the BHS and industry). This in AONBs, villages, National Parks.

            3. Yield ratios are expected to be low and the damage from industrialisation high, with the well density required to produce from these rock types.

            4. The far higher levels of energy needed for extraction from unconventional sources plus the large amount of contaminated and highly salinated water that will also need energy to treat it lead some wastewater experts to believe there’s likely to be little if any net gain, unless of course the wastewater, including NORMs from these formations, isn’t disposed of safely.

            5. We have the benefit of a huge amount of medical and environmental information from the USA on the impacts of unconventional extraction. Let’s just say here the picture isn’t rosy.

            I can offer you links to support the above points if you have any doubts, but not until I’m home from our family holidays.

            Incidentally I notice plenty of ex North Sea oil and gas industry workers now in campaign groups, working hard against this onshore unconventional exploration.

            • Hi Dorkinian, enjoy your holiday. Don’t worry about all this. My points are made to show that the FOE position on acidising and their doomsday outlook is incorrect. There are no problems associated with the execution of oil and gas well acid stimulations. The risks are to the workers handling the acid on the rig site and there are proper procedures in place for this. Transport of acid (HCl) may also be a risk but this is a risk whatever the end use is going to be.

              Your point 1 is irrelevant, the UK can stop using hydrocarbons today and it won’t make any difference globally. And there is nothing wrong with using oil and gas from closer to home to offset imports, including the North Sea and onshore UK. We were acidising in Hampshire in the 1980s – no fuss made then.

              Your points 2 – 4 are relevant in that if proven correct will make the development too expensive and none commercial so it won’t happen. If you are correct about the high drilling density then this will also stop the development as planning permission will not be granted. Personally I don’t expect any large developments in the Weald or shale gas in the NW – unless the flow rates and decline curves are very good (which we will know in a few months).

              Point 5 Please don’t post any more links from the US – there are already a few “specialist” posters on this BB.

              • Hi Paul,

                Thank you, I will.

                Can’t agree with your fatalistic attitude to my point 1, the Paris Agreement can work, but large economies like the UK must be seen to be complying.

  7. Click to access acidizing-oil-natural-gas-briefing-paper-v2.pdf

    Oil and gas operators have safely and successfully used acid to improve productivity of oil and gas wells for nearly 120 years. Today, acidizing is one of the most widely used processes for stimulating oil and gas wells.

    Two types of acids are most commonly used; hydrochloric acid in all formation types and hydrofluoric acid in sandstones and certain shales. Other types of acids, such as organic acids, may also be used in specialized situations.

    Since geologic formations are never homogeneous, blends (particularly for sandstone formations) of HCl and HF are usually pumped with the blend ratios based on the formation mineralogy.

    All aspects of the regulatory framework surrounding the use of acid in oil and gas wells are well developed and mature as are the operational and safety practices employed by operators and service providers.

    When the acid reacts with formation materials it is largely consumed and neutralized.

    Spent acid that is recovered when a treated well is brought on production is treated and safely disposed of in essentially the same way as produced water.

    Please forward to Friends of the Earth as they clearly need help….

  8. As well as (a) ban, Friends of the Earth called for:

    An assessment of the health and environmental impacts of acid well stimulations in England
    Identification of chemicals of concern used in all onshore well stimulation operations
    Government publication of data on the number and type of acid stimulations in England
    A requirement for exploration companies to state explicitly in planning applications whether they want to use acid and for what purpose.

    If acid is banned why do they want all the other information? FOE, the usual BS……

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